A water-developable plate is a plate in which a photosensitive layer is hydrophilic before exposure and a relief image is formed by crosslinking an image-forming area by the exposure. Accordingly, the plate is subjected to a developing treatment after the exposure (removal of unexposed area of the photosensitive layer) with water or an aqueous alkali solution. On the other hand, a solvent-developable plate requires a developing treatment after exposure using an organic solvent, which is troublesome in handling. Therefore, the water-developable plate which is more simple in the developing treatment has become predominant as a plate for use in letterpress.
On the other hand, the plate is in the form of a sheet and usually has a structure of covering both surfaces of photosensitive layer of a predetermined thickness comprising a photosensitive resin composition with protective films. In transportation and storage, a plurality of sheet-like plates are laminated and a laminate is packaged with a light screening film and placed, for example, in a corrugated board box. The water-developable plate involves a problem of causing deformation in the plate during transportation or storage at a high temperature and a high humidity in summer.
It is considered that the problem is attributable to easy moisture absorption since the photosensitive layer of the water-developable plate is hydrophilic. Therefore, for preventing moisture absorption of the water-developable plate at a high temperature and a high humidity in summer, the following countermeasures have been adopted in the prior art. That is, in a case of a solvent-developable plate, when a laminate of plates are packaged with a light screening film 4 into a package 6, only the packaging ends are secured at several positions by tapes 5, for example, as shown in FIG. 3(a), but in a case of a water-developable plate, all of the portions through which moisture can intrude are secured with a tape 5, for example, as shown in FIG. 3(b). Alternatively, the humidity is lowered in a transportation environment or a storage site for the package.
However, the package of the plates are usually packaged on every about ten sheets with a light screening film and they are used in most cases such that about two or three sheets of them are taken out per one day while other remaining plates are stored. Accordingly, in the countermeasures described above, a method of securing all the portions of the light screening film through which moisture can intrude complicates the tape securing operation after taking out the plates.
As a method of avoiding this complication, it may be considered to package plates sheet by sheet. However, since this requires the stringent packaging described above on each sheet for all plates, the operation upon packaging is troublesome. Further, the countermeasure for lowering the humidity in the transportation circumstance or the storage site of the package involves a problem in view of the cost and reliable moisture proofness.
The present invention has been accomplished taking notice on such problems in the prior art and it is a subject thereof to prevent occurrence of deformation of the plates in a package in which water-developable plates are packaged in a laminated state during transportation or storage at a high temperature and a high humidity in summer, without complicating the operations at the time of use or packaging of plates and without increasing the cost remarkably.